1. Field of the Invention
The present invention relates to a driving unit for use in an electric assist bicycle, and an electric assist bicycle including the driving unit.
2. Description of the Related Art
Recently, electric assist bicycles have been disclosed that assist the rider by augmenting the pedaling force of the rider (hereinafter referred to as “tread force”) with a driving force of an electric motor. An electric assist bicycle includes a torque detection device. The torque detection device measures the torque generated in the crankshaft when the rider pedals the bicycle. When a torque larger than a predetermined reference value continues to be generated for a certain period of time, the electric assist bicycle assists the rider by augmenting the tread force with a driving force by the electric motor.
Some electric assist bicycles include a rotation detection device to detect rotation of the crankshaft, in addition to a torque detection device. For example, JP-Hei 8-58670 A discloses an electric assist bicycle including a tread force detection device and a crankshaft rotation sensor. The tread force detection device includes a torque/displacement converting device that converts torsion by a tread force into an axial displacement and a stroke sensor that outputs an electric signal corresponding to the displacement. The torque/displacement converting device works by engaging the convex cam surface provided on the end surface of a slider inner side that rotates together with the crankshaft with the concave cam surface provided on the end surface of the driving member. The crankshaft rotation number sensor detects, in an optical or magnetic manner, a cog provided on the periphery of a collar that couples the crankshaft with the head of the torsion bar and outputs a detection pulse.
As discussed above, the electric assist bicycle assists the rider by augmenting the tread force with the driving force from the electric motor. To assist the rider in a manner that corresponds to the pedaling of the rider, for example, a rotation detection device may be provided in addition to a torque detection device, and the detection resolution of the rotation detection device may be increased.
In JP-Hei 8-58670 A, the number of cogs must be increased in order to increase the detection resolution of the crankshaft rotation sensor. However, in JP-Hei 8-58670 A, the cogs are provided on the collar that couples the crankshaft with the head of the torsion bar. As such, it is unrealistic to increase the number of cogs to increase the detection resolution.